Research progress and prospect of Fe−Mn−Al−C medium Mn steels

As vehicle ownership increases, the trend lightweight design puts energy consumption and environmental concerns on automotive steel. The research concept of the third generation of automotive steel currently under development is to combine the addition of lightweight elements with “light” and improve plasticization with “thin”. Some of the research hotspots are Fe−Mn−Al−C medium Mn steels as the main component of the third generation of automotive steel. This paper summarized the research literature of Fe−Mn−Al−C steels in recent years in different countries, and discussed the advantages of Fe−Mn−Al−C medium Mn steels in terms of production cost and mechanical properties; the mechanical properties of that is not worse or even better than the second generation of advanced high-strength automotive steel such as TWIP steel can be obtained under the premise of cost savings. The literature was reviewed from the aspects of composition design, process design, microstructure characteristics, deformation and fracture mechanism, and the effect on the efficiency of chemical composition, process route, and microstructure on performance was summarized. It proposed a reasonable range of chemical elements especially Mn and Al, and compared the focus of the two different process routes (Intercritical annealing and quenching + Tempering). The deformation mechanism of medium Mn steel, especially transformation-induced plasticity (TRIP) effect, and the stacking fault energy and austenite stability were identified, in particular, the factors affecting the austenite stability such as grains size, grain morphology and chemical elements were described, and the three-stage work hardening behavior that often occurs in Fe−Mn−Al−C steels was explained. Furthermore, the literature proposed suggestions on regulating the organization of Fe−Mn−Al−C steels by studying the fracture mechanism of materials. Typically the initiation of cleavage cracks is linked to the process of coarse δ-ferrite and κ* phase. Finally, this paper summarized the controversial issues in Fe−Mn−Al−C medium Mn steels research and prospected the future development trend, to provide a reference for the follow-up research and actual production of medium Mn steels.